Geographic Information System: Maps Definition

GEOGRAPHIC INFORMATION SYSTEM

MAPS DEFINITION

A map is a set of points, lines and areas that are defined by their spatial location with respect to a coordinate system and by their non-spatial attributes? (Burrough 1986). A map legend links the non-spatial attributes to spatial attributes.

Types of Maps

There are three different types of maps, they are :

(i) General - purpose maps

They do not show any feature with special emphasis - they usually show roads, power lines, transportation routes, water features etc.

(ii) Special Purpose Maps

They are made for specific purposes such as ocean charts for navigation, cadastral maps to show property ownership details. They are usually of a large scale, which means a smaller portion of the earth.

(iii) Thematic maps

A map, which has a particular geographic theme. In a GIS the roads, rivers, vegetation, contour elevations etc, are categorized separately and stored in different map themes or overlays.

There are two different types of thematic maps, they are :

(i) A choropleth Map

A choropleth map contains different zones. The different zones are used to represent the different classes present in a theme for example,

Theme : census tracts class : average income, percentage, female populations, mortality rate etc.

(ii) An isopleth Map

An isopleth map is a map, which contains imaginary lines used to connect points of equal values. (Isolines) They may be contours in the case of a topographic map. Similarly maps can be drawn for variables such as temperatures, pressure, rainfall and population density.

Uses of Maps

1.  Maps have been around since ancient times where they were originally used for navigation and military purposes.

2.  Maps are used to organize geographic data. The geographic data are :

A.                        Topography

General in nature.

B.                        Natural resources

?Thematic maps?, contains information about a specific subject or theme (geology, soils, roads, ecology, hydrology… etc.).

C.                        Political

?Abstract? boundaries for public, private, national and international lands.

D.                        Information types

Qualitative - land use classes.

Quantitative        -   depth    to bedrock.

Characteristics of Maps

The following are the characteristics of maps, they may be of any type but they all have the same characteristics.

1.              Maps are always concerned with two elements of reality

a)                                      One is the location, which is the special data.

b)                                     The attributes concerned with it, which are referred to as a spatial or non spatial data..

2.              Maps are usually outdated representations. This is because yesterday's reality need not be true today also.

3.              Maps are always static versions i.e., they are permanent prints on paper, in which alterations or changes cannot be made.

4.              Maps cannot be updated with the same version in other words, updating a map involves the preparation of a new map.

5.              Maps are always drawn to some scale, smaller the scale more detailed will be the map.